1. Field of the Invention
The present invention relates to a driving assistance system, an image processor, and an out-of-position detection method in which: peripheral views of a vehicle are imaged by a plurality of vehicle cameras; and a plurality of images thus imaged are converted into projection images projected on a plane while the projection images projected on the plane are synthesized to generate a synthesis image.
2. Description of Related Art
Heretofore, driving assistance systems to allow a driver of a vehicle or the like to monitor a peripheral situation of the vehicle have been disclosed, for example, in Japanese Patent Application Laid-open Publication No. 2002-87160. In this driving assistance system, a peripheral view of a vehicle is imaged using a plurality of vehicle cameras mounted on a periphery (e.g., on the left, right, front, and rear sides) of the vehicle, and images thus imaged are displayed on a display panel.
In such a driving assistance system, images produced by imaging a vehicle periphery are each converted into projection images projected on a plane (e.g., ground or the like). Further, a plurality of converted projection images are synthesized so that a synthesis image (a peripheral bird's-eye image) showing a vehicle viewed from an imaginary point in the sky is generated, and displayed on a display panel. Accordingly, the driver can check at a glance the situation around the vehicle from the synthesis image displayed on the display panel. In addition, the above driving assistance system is configured to synthesize projection images according to parameter values calculated in advance by adjusting and setting (calibrating) the positions and imaging directions (camera directions) of the respective vehicle cameras, when generating a synthesis image.
Incidentally, an vehicle camera mounted on a vehicle sometimes moves out of its proper position, imaging direction, or the like due to external forces such as vibrations during driving. In such cases, the parameter values become no longer suitable values, so that a generated synthesis image has parts of projection images synthesized out of their correct positions. Consequently, the generated image is not adequate for the driver to check the peripheral situation.
There is a generally-known method as a method for automatically evaluating whether a vehicle camera has moved out of its proper position. In this method, a plurality of vehicle cameras are disposed to image a target region (overlapping region) in an overlapping manner, and then obtained images of the overlapping region are compared.
More specifically, referring to FIG. 12, a driving assistance system including vehicle camera 10_1 and vehicle camera 10_2 is described as an example. Incidentally, a projection image of an image imaged by vehicle camera 10_1 is denoted by projection image E1, and a projection image of an image imaged by vehicle camera 10_2 is denoted by projection image E2. Further, projection images E1 and E2 are each assumed to include an image corresponding to overlapping region C.
In the driving assistance system, as shown in FIG. 12, for example, edges of white lines M1 and M2 painted on the road, or something a similar object are detected as discriminative points from an image corresponding to overlapping region C of projection image E1 and projection image E2. Further, when a plurality of projection images are overlapped and synthesized, the positions of edges of white lines M1 and M2 are compared. If a difference therebetween is large, it can be detected that a vehicle camera has moved out of its proper position.
However, in the aforementioned driving assistance system, even when a vehicle camera has not moved out of its proper position, a difference sometimes occurs in an image on an overlapping region of projection images.
For example, as shown in FIG. 13, when there is solid object P such as a pole in overlapping region C, in the driving assistance system described above, vehicle cameras disposed on different positions image solid object P from different directions. Further, when the images are converted into projection images E1 and E2, information on a height direction of solid object P is lost. Consequently, images of solid object P contained in the projection images E1 and E2 projected on a plane become images Pa and Pb, respectively, which are different from each other.
In this case, when edges of the images Pa and Pb of the solid object are set as discriminative points, a difference between images corresponding to an overlapping region in projection images E1 and E2 becomes large. In other words, when there is a solid object in overlapping region C, the above-described driving assistance system has a problem of failing to accurately detect whether a vehicle camera has moved out of its proper position, by use of the difference of the images corresponding to overlapping region C.